GENOME AFFINITIES AND EPITOPE PROFILES OF WHITEFLY-TRANSMITTED GEMINIVIRUSES FROM THE AMERICA

The relationships among fifteen isolates of whitefly-transmitted gemin iviruses (WTGs) from North, Central and South America and six from oth er continents were assessed (a) in nucleic acid hybridisation tests wi th sulphonated DNA probes for eight of the viruses, and/or (b) in trip le-antibody-sandwich ELISA with panels of monoclonal antibodies (MAbs) to particles of African cassava mosaic virus (ACMV) and Indian cassav a mosaic virus (ICMV). Probes specific for DNA-A of four American viru ses, abutilon mosaic (AbMV), bean golden mosaic (BGMV), squash leaf cu rl (SLCV) and tomato golden mosaic (TGMV), detected virtually all the American viruses but reacted weakly if at all with ICMV, ACMV or tomat o yellow leaf curl virus from Thailand (TYLCV-T). Conversely, the prob e for ACMV DNA-A did not detect any of the American viruses, and that for TYLCV-T DNA-A reacted weakly with SLCV and TGMV but did not detect the others. In contrast, probes specific for DNA-B of the four Americ an viruses or ACMV detected only the homologous virus, except for slig ht reactions between the AbMV DNA-B probe and both chino del tomate vi rus (CdTV)-DNA and SLCV-DNA. However, a probe for DNA-B of bean calico mosaic virus (BCMoV) reacted weakly with BGMV-PR DNA, and a probe for DNA-B of CdTV from Mexico detected several American viruses. Six out of 17 MAbs specific for ACMV and six out of 10 MAbs specific for ICMV reacted with one or other of the 14 American virus isolates tested. Tw o anti-ACMV MAbs reacted with all, and one anti-ACMV MAb and two anti- ICMV MAbs reacted with nearly all the American viruses, one anti-ACMV MAb reacted with about half the American viruses and six other MAbs re acted with only one or two of them. Of the American viruses, CdTV and AbMV were the least closely related to the others. The epitope profile s of BCMoV, BGMV, cotton leaf crumple virus, serrano golden mosaic vir us and SLCV were virtually indistinguishable. TGMV, potato yellow mosa ic virus (PYMV) and an euphorbia virus had profiles intermediate betwe en those of the BGMV cluster and AbMV-CdTV. In general, the epitope pr ofiles and the results of hybridisation tests with DNA-A probes show t hat the similarities among the American viruses are greater than those between the American viruses and the viruses from other continents; t he hybridisation tests with DNA-B probes show that substantial differe nces exist between individual American viruses. In America, geminiviru s evolution seems to have proceeded convergently from different progen itor viruses, or divergently from one ancestral form, with DNA-B diver ging to a greater extent than DNA-A and its particle-protein gene.